Such wheel suspensions with partial load-bearing, active suspension means with a bearing spring and a preloaded spring and an electric actuator for automatic leveling and dynamic ride control of the body of the motor vehicle are known, cf., e.g., DE 199 55 410 A1. An electromagnetically-actuated brake or lock that secures the adjustment drive in the respectively set position there can be provided on the adjustment drive of the actuator.
In the known wheel suspension, the adjustment of a spring seat, on which both the bearing spring and the preloaded spring are supported on both sides, is carried out with an electric motor on a ball screw. The common spring base of preloaded spring and bearing spring is altered in its height position according to dynamic performance requirements. Thus, the electric motor must be constantly loaded with more or less current. When the motor vehicle is shut off, a certain quiescent current must also flow in this instance in order to ensure that the motor vehicle remains at a constant height. When the current is interrupted, the motor vehicle, corresponding to its temporary load condition, would sink until a static equilibrium between bearing spring or preloaded spring prevailed. If the motor vehicle were accidentally to be located over an obstacle, for example a curb, subsequent damage is possible. Thus, for example, the oil pan or the body could be damaged.
Moreover, not only must the electric motor of the height adjustment device be locked when the motor vehicle is shut off, but also in the event that various error conditions occur in normal driving. Thus, in the event that a control signal of the motor vehicle regulator is not present or is false, it has to be ensured that the electric motor comes to a halt in the middle position of the adjustment travel and is also held by the stop.
The object of the invention is to propose an adjustment device of the generic type that makes greater allowance for the safety and functional requirements when the motor vehicle is driven normally.